This invention relates to coated aramid fibers for cement reinforcement and to fiber-reinforced cement products incorporating such fibers. The combination of such coated aramid fibers with a pulp of oriented polyethylene fibrids is particularly useful for this purpose.
Substantial activity is being directed to developing reinforcing fibers for cement which replace the asbestos fibers formerly used. Cellulose fibers are being used for this purpose because of their capacity for dispersing in cement slurries to form webs in the manufacture of fiber-reinforced cement products. However, cellulose fibers are susceptible to swelling and degradation in the alkaline cement medium and this tends to reduce their performance as a reinforcement. Certain efforts have been made to overcome these deficiencies (see International Publication No. WO 84/03275).
The use of a pulp of oriented polyethylene fibrids having a birefringence of at least about 0.030 for cement reinforcement has been disclosed in a copending, coassigned U.S. Appl. Ser. No. 756,705. The addition thereto of staple fiber such as p-aramid fiber to increase flexural toughness of the cement composite is also disclosed in said copending application.